Stopping flicker during updates

When making major changes to a list control (and other controls) it is a good idea to turn off updating of the control. To do this you would use SetRedraw(false) at the start of the change and SetRedraw(true) at the end, and then invalidate the control.

However, SetRedraw simply turns redraw on or off, it does not let you know whether or not redraw was on or off before the call. And there is no function that can tell you this.

For this reason, I have my own SetRedraw function that counts the number of times you have turned it on and turned it off.

Define a member variable:
     int m_redrawcount;

In your contructor do:

     m_redrawcount = 0;

And then define the following function (in this case for a list control):

void CMyListCtrl::SetRedraw( BOOL bRedraw) {
     if (! bRedraw) {
          if (m_redrawcount++ <= 0) {
               CListCtrl::SetRedraw(false);
          }
     } else {
          if (--m_redrawcount <= 0) {
               CListCtrl::SetRedraw(true);
               m_redrawcount = 0;
               Invalidate();
          }
     }
}

The first time you turn redraw off, the real SetRedraw function is called to turn redrawing off. Subsequently the function increases a counter when you requested redraw be turned off, and decreases it when you request redraw to be turned on again. When the counter gets back down to zero, the real SetRedraw function is called to turn redrawing back on again and the control is invalidated (so that redrawing actually takes place).

This means you can not put SetRedraw(false) at the start of, and SetRedraw(true) and the end of, any function that makes large changes to the lsit control (like loading, sorting, changing with column widths or order etc).



Comments

Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • Lenovo recommends Windows 8 Pro. "I dropped my laptop getting out of the taxi." This probably sounds familiar to most IT professionals. If your employees are traveling, you know their devices are in for a rough go. Whether it's a trip to the conference room or a convention out of town, any time equipment leaves a user's desk it is at risk of being put into harm's way. Stay connected at all times, whether at the office or on the go, with agile, durable, and flexible devices like the Lenovo® …

  • U.S. companies are desperately trying to recruit and hire skilled software engineers and developers, but there's simply not enough quality talent to go around. In response, companies often resort to inferior solutions -- hiring substandard developers and engineers, recruiting talent on a part-time or temporary basis, poaching people from competitors, or burdening an already stressed IT staff for more of their labor. Fortunately, there's a better solution. Read this white paper to learn the business value of …

Most Popular Programming Stories

More for Developers

RSS Feeds

Thanks for your registration, follow us on our social networks to keep up-to-date